This invention refers to a procedure to identify coins, based upon their mechanical features, and more specifically based upon the sound issued whenever the coin being analyzed hits a hard surface.
Many procedures for the identification and classification of metal pieces, such as coins and tokens, which use signals supplied by electronic sensors, particularly of the electromagnetic, optical and extensometric types, are currently known. The analysis of the coin is effected whilst it rolls and passes sequentially through the various sensors.
Also known are devices used to analyze vibrations issued when the coin hits a hard surface. The kinetic energy of the coin generates vibrations, both within the coin itself and upon the area subject to the impact. An analysis of those vibrations may yield an indirect measurement of the characteristics, characteristics related to the size and weight of the coin.
Thus, patent number ES 8,308,113 (Meyer) describes a piezoelectric sensor in which the impact of the coin results in an electrical output corresponding to its elasticity.
U.S. Pat. No. 4,848,556 (Qonnar) does also use a piezoelectric sensor that is subjected to the impact of a coin, from which a measurement of the mass of the coin may be obtained.
Patent number ES 9002855 (Mars) uses a piezoelectric sensor fitted near the coin impact area and which is sensible to the high frequencies generated by the impact upon the element against which the coin collides. These vibrations are then transferred to the piezoelectric sensor through the frame of the coin discriminator itself.
The patents mentioned above analyze the vibrations at the impact area, generated by the collision of the coin. There are also procedures to analyze the vibrations generated within the coin itself following the impact, based upon a study of the acoustic signal issued by the coin after the impact. Patents number DE 2017390 and U.S. Pat. No. 5,062,518 may be quoted as significant examples.
Patent number 2017390 describes a procedure used to analyze the sound issued by the coin which signal is being studied using a microphone located near the impact area, determining the acceptability of the coin as a function of the appearance or non appearance of a frequency characteristic for each denomination.
U.S. Pat. No. 5,062,518 (Plessey) describes a coin discriminating device that analyzes the sound of the coin shortly after its impact, obtaining the spectrum in a wide range of frequencies and determining the acceptability of the coins as a function of the appearance or non appearance of their expected frequencies, different for each type of coins.
Both the devices that analyze the vibrations induced by the coin upon the impact area and those that analyze the vibrations of the coin itself present drawbacks that have caused their use to be very significant. Specifically, the systems described by patents ES 8308113 and U.S. Pat. No. 4,848,556 require that the coins impact upon the sensor from a well defined height and without any dampening within their trajectory prior to the impact, conditions that are difficult to achieve in practice.
Patent number ES 9002855 describes a device of the type mentioned in the two prior patents, but which is less sensible to the height from which the coin drops down to the impact surface. This device is nevertheless valid only to discriminate elasticity counterfeit alloys, or else forgeries that incorporate a ring made of a soft material around them.
Patents number DE 2017390 and U.S. Pat. No. 5,062,518, which analyse the sound spectrum of the coin for its identification, have as a drawback that the coin, depending upon the angle of incidence, drop height or even the specific coin impact point, does not always produce the same sound signal. Even in the most favourable mechanical arrangement case, it would require a complex electronic device to precisely discriminate the various frequencies that characterize the different types of coins, often closely related to each other.